A wide range of medical procedures involve placing objects, such as sensors, tubes, catheters, dispensing devices and implants, within a patient's body. Position sensing systems have been developed for tracking such objects. Magnetic position sensing is one of the methods known in the art. In magnetic position sensing, magnetic field generators are typically placed at known positions external to the patient. A magnetic field sensor within the distal end of a probe generates electrical signals in response to these magnetic fields, which are processed in order to determine the position coordinates of the distal end of the probe. These methods and systems are described in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612, 6,332,089 and 6,690,963, in PCT International Publication WO 1996/005768, and in U.S. Patent Application Publications 2003/0120150 A1 and 2004/0068178 A1, whose disclosures are all incorporated herein by reference.
When placing a probe within the body, it may be desirable to have the distal tip of the probe in direct contact with body tissue. The contact can be verified, for example, by measuring the contact pressure between the distal tip and the body tissue. U.S. Patent Application Publications 2007/0100332, 2009/0093806 and U.S. Pat. No. 8,535,308, whose disclosures are incorporated herein by reference, describe methods of sensing contact pressure between the distal tip of a catheter and tissue in a body cavity using a force sensor embedded in the catheter.
Some probes include both a force sensor and a position sensor. U.S. Pat. No. 8,523,787, whose disclosure is also incorporated herein by reference, describes a method for detecting tenting in tissue (due to a force exerted by the distal tip of the probe on the tissue) using location and force measurements received from a probe that includes a position sensor and a force sensor.
Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.